Immersion heating apparatus



United States Patent 12 Claims ABSTRACT OF THE DISCLOSURE A tubular heating unit is mounted within a furnace adapted to contain liquid metal. The heating tube is supported with an inlet and an outlet above the normal operating level of the bath and an intermediate portion immersed within the bath. A flame producing nozzle mounted within the inlet directs the heating flame through the intermediate portion of the tube and toward the outlet. A short tubular shield surrounds the nozzle at the inlet and forms a dead air space to locally insulate the heating tube at and above the normal operating level of the bath. A ceramic liner mounted within the outlet provides calized insulation for that portion of the heating tube associated with and above the normal operating level of the bath at the outlet and cooperates with the heating tube to form a socket for a removable exhaust stack.

CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of application Ser. No. 478,889, filed Apr. 11, 1965 now abandoned.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to apparatus for metal heating and treating furnaces and more particularly to an improved tubular immersion heating unit for a heating flame with localized insulation for reducing corrosion and improving the life of the tubular member.

Description of the prior art Immersion heating furnaces are commonly employed as a means for heating and melting metals such as zinc and the like. Typically such a melting apparatus takes the form of a heating furnace having a chamber or reservoir for containing a liquid bath of the molten metal. A tubular heating unit is immersed in the reservoir and a heat-producing flame produced by a burner is directed through the tube which transfers the heat to the metal.

Normally the burner nozzle delivers a flame which extends to an area just short of the full length of the heating tube. There are two areas of short life normally associated with conventional heating tubes. These are those areas of the heating tube above the normal operating level of the bath for it is these areas which are the hottest and which are attacked by the metal being heated. Thus, the inlet to the heating tube in the vicinity of the operating level of the bath is exposed to the full heat of the flame as it is discharged from the burner nozzle. Simila rly, the discharge end of the heating tube in the vicinity 3,439,618 Patented Mar. 4, 1969 "ice of the normal operating level of the bath is exposed to the hot exhaust gases resulting from the fiame and without a sufficient heat dissipating effect of the bath corrosion results.

These areas of heat concentration substantially reduce the life of conventional heating tubes and require their frequent replacement. This is in part because these particular areas of the tube are exposed to various corrosive influences of the metal that are normally near the surface of the bath and produced by various impurities in the atmosphere adjacent the level of the bath. The high temperature of the heating tube in these areas also tends to accelerate the corrosive process.

The conventional approach toward prolonging the life of immersion tubes is to provide some sort of insulating liner or insert at the inlet of the heating tube which surrounds the burner nozzle and shields the heating tube adjacent the nozzle from the full effect of the heating flame. This approach is illustrated in British Patent No. 687,303, published Feb. 11, 1953. The present invention aims to provide a heating tube having improved means for locally insulating the tube both at the inlet and outlet in those areas associated with the normal operating level of the liquid bath in order to extend the effective life of the tube, and furthermore to provide an improved means for delivering the products of combustion of the heating flame from the bath in order to improve the quality of the metal.

SUMMARY The preferred embodiment of the present invention, which will be subsequently described in greater detail, takes the form of a heating furnace having a reservoir for containing a liquid bath of metal. A tubular heat transfer member or heating tube is mounted in the furnace reservoir with its inlet and outlet extending above the normal level of the bath and an intermediate portion submerged in the bath. A burner nozzle mounted within the inlet is adapted to deliver a heating flame the length of the heating tube toward the outlet, the tube transferring the heat of the flame to the metal bath.

A short tubular shield is mounted within the inlet and surrounds the burner assembly. The lower end of the shield extends below the normal operating level of the bath so that it prevents the flame from contacting the heat transfer tube in the vicinity of the operating level of the bath, thereby reducing the heat concentration in this area.

An air space is formed around the shield and within the inlet of the heat transfer tube. The upper end of this air space above the bath level is closed so that a dead air space cooperates with the shield to insulate that portion of the heating tube associated with the baths operating level from the full heating effect of the flame.

This dead air space provides an important improvement over the prior art in significantly prolonging the elfective life of the heating tube. Conventional heating tubes having a nozzle-protecting shield permit the circulation of the hot gases through the opposite open ends of the shield. The preferred embodiment of the present invention closes the upper end of this air space thereby reducing the average eifective temperature of the heating tube inlet.

Preferably the inner diameter of the air space is of the outer diameter and about twice the diameter of the burner nozzle. This diameter ratio is important in that if the diameter of the shield is increased in size to approach the inner diameter of the heating tube, the insulating effect 3 of the air space is reduced. Similarly if the diameter of the shield is substantially reduced so that this ratio is reduced, the heating flame does not contact those sections of the heating tube in the direction of flow of the combustion products that are not intended to be shielded by the tubular shield.

Thus, both the shield and the annular dead air space provided localized insulation for the inlet of the heating tube. This is a significant improvement over the aforementioned British patent which substantially provides an elongated insert for shielding the flame but is of such a length that it reduces the effective heating surface of the heat transfer tube.

A ceramic sleeve or liner mounted within the exhaust end of the heating tube with a length accommodating the upper and lower operating levels of the bath insulates the heating tube at the outlet from the full effect of the hot exhaust gases thereby preventing undesirable heat concentration in this area. The upper end of the ceramic liner terminates below the upper end of the heating tube to form a socket for a removable exhaust stack.

The preferred exhaust stack has a lower reduced end section which is seated in the socket. This novel arrangement permits the stack to be easily removed and replaced. In addition, a removable stack arrangement allows the stack to be made of relatively cheap material such as cast iron as opposed to the relatively expensive alloys necessary for the heating tube.

The stack is preferably long enough to remove the combustion products of the heating flame to an area remote from the bath. This feature is essential for such metals as zinc and where the heating fuel has an excess of air so that the combustion products contaminate the metal if expose to the bath.

It has been found that the preferred heating tube has an effective life approximately double the life of conventional heating tubes. This increased life is due to the improved means EfOl' locally insulating those areas of the heating tube which are normally exposed to severe, lifereducing corrosive influences normally associated with the bath level and above.

It is therefore an object of the present invention to extend the effective operating life of immersion type heating tubes employed for melting zinc or the like by providing improved means for insulating those areas of the heating tube normally most severely exposed to the corrosive influences associated with the operating level of the heated metal.

It is another object of the present invention to improve immersion type tubular heating apparatus for melting or heating metals such as zinc or the like by providing a tubular heating unit having a heating portion normally submerged in a liquid bath of the metal and a flame Outlet above the bath level, means for delivering a heatproducing flame through the heating tube and towards the outlet, an insulating liner mounted within the outlet of the heating tube and arranged to insulate that portion of the outlet associated with the operating bath level from the flame, the insulating liner terminating short of the heating tube to cooperate with the heating tube to form a socket for a removable exhaust stack.

Still another object of the present invention is to extend the life of immersion type heating tubes, having a flame producing burner mounted in the inlet for directing a flame through the length of the heating tube by providing a shield for surrounding the burner and to form a dead air space between the burner nozzle and that portion of the heat transfer tube associated with the normal operating level of the bath.

Still further objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains upon reference to the following detailed description,

4 DESCRIPTION OF THE DRAWING The description refers to the accompanying drawing in which like reference characters refer to like parts throughout the several views and in which:

FIG. 1 is a cross-sectional view of the preferred immersion heating apparatus in which portions of a preferred fuel system are illustrated schematically, and

FIG. 2 is a plan view of the apparatus of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Now referring to the drawing, a preferred immersion heating apparatus is illustrated as comprising a furnace 10 having a reservoir 12 for containing a liquid bath (14 of the metal which is to be heated or melted. FIG. 1 illustrates the normal operating level of the bath.

A burner assembly 16 having a pilot burner 18 is mounted on the furnace 10 by a support member 20. The preferred fuel system for the burner assembly comprises a compressor 22 for delivering compressed air to an air inlet 24 provided in the burner assembly 16 through a conduit 26. A valve 28 in the conduit 26 controls the air flow and is actuated by a control motor 30. The burner assembly 16 also has a gas inlet 32 connected to a source of gaseous fuel by a conduit 34. A gas-air ratio regulator 38 connected in the conduit 34 has an air inlet 40. A branch conduit 42 provides a connection between the conduit 26 and the air inlet 40. A limiting orifice gas valve 44 in the conduit 34 is between the regulator 44 and the gas inlet 32.

A substantially U-shaped heat transfer member 46 is mounted on the furnace 10 by a bracket 48 and the support member 20. The heat transfer member 46 has an inlet 50 and an outlet 52 supported above the normal operating level of the bath :14 and an intermediate portion 54 submerged within the bath.

A tubular shield 51 depends downwardly from the support member 20 and concentrically into the inlet end 50 of the heat transfer member 46. The tubular shield preferably has a diameter approximately 80% of the inner diameter of the heating tube 46 so that an annular air space 53 is formed between the heating tube 46 and the shield 51. The shield 51 extends downwardly a distance slightly below the lower limit of the normal operating level of the bath 14.

The annular air space 53 is closed at its upper end by a plate 55 supported by the member 20.

The burner assembly 16 includes an upper housing 56 positioned above the reservoir 12 and mounted to the plate 55 and a tubular conduit 58 which extends downwardly through the plate 55 and into the shield 51 and terminates in a nozzle 60. The lower end of the nozzle is spaced downwardly from the lower or free end of the shield 51 so that the shield 51 prevents the flame from coming into contact with that portion of the heating tube 46 above the normal operating level of the bath 14 thereby reducing heat concentrations in this area. The annular dead air space 53 provides localized insulation for the heat transfer member 46 at and above the operating level of the bath thereby extending the useful life of the heating tube 46.

The preferred heat transfer member 46 has a much longer useful life than conventional heat transfer tubes particularly when employed as a means for transferring heat to zinc at high temperatures. Zinc has a tendency to combine with atmospheric elements to produce an excessively high corrosive influence tending to cause tube burnout. This problem is particularly acute in conventional apparatus when the operating level of the bath 14 is lowered so that the nozzle 60 produces a flame above the level of the bath 14.

A tubular insulating liner 62 is positioned within the discharge or exhaust end 52 of the heat transfer member and has a length accommodating the variations in the operating level of the bath 14 so that it insulates the heat transfer tube at and above the bath level from the hot exhaust gases of the heat-producing flame.

Preferably the liner 62 is constructed of a ceramic material for it has been found that metallic insulators tend to get too hot and burn out. The lower end of the liner 62 while it does extend below the normal operating level of the bath 14 this extension is kept to a minimum so that the liner 62 does not substantially reduce the heat transfer surface of the heat transfer tube 46.

The upper end 64 of the liner 62 terminates short of the upper end of the discharge end 52 of the heat transfer tube 46 and cooperates with the heat transfer tube 46 to form a socket for supporting a removable exhaust stack 66. The exhaust stack 66 has a reduced portion 68 which is received within the discharge end of the heat transfer tube 46 so that the lower end of the exhaust stack seats against the upper end of the liner. Preferably, the exhaust stack 66 has an annular shoulder 70 spaced upwardly from its lower end which seats against the extreme upper end of the discharge end 52 of the heat transfer tube.

This mounting arrangement for the exhaust stack 66 permits the exhaust stack 66 to be easily removed and replaced in a fairly simple mounting structure and also permits the exhaust stack to be formed of a relatively inexpensive material such as cast iron as opposed to the relatively expensive alloys from which the heat transfer tube 46 is made. It can be seen that the inner diameter of the exhaust stack 66 is similar with the inner diameter of the liner 62 so that the exhaust stack provides an upward continuation of the inner surface of the insulating liner 62. The exhaust stack 66 has a length sufiicient to discharge the products of combustion of the heat produced by the flame in an area removed from the bath 14. This is particularly important with certain metals such as zinc wherein the combustion products tend to accelerate oxidation of the zinc when they come into contact with the surface of the bath. This oxidation reduces the purity of the zinc.

It is apparent that I have described an improved heating apparatus for an immersion bath which substantially extends heating tube life over that of conventional heating apparatus because the inlet and outlet portions of the heating tube which are normally subjected to highly corrosive influences under extreme temperatures are locally insulated. This localized insulation is provided by the dead air space in cooperation with the tubular shield surrounding the burner assembly at the inlet of the heat transfer tube and the ceramic insert or liner which is mounted within the discharge end of the heating tube.

In addition, I have described a relatively simple structure for mounting a removable exhaust stack which takes the form of a socket formed by the insulating liner and the extreme discharge end of the heat transfer tube. Thus, the quality of the metal treated in the preferred melting apparatus is improved by the functioning of the exhaust stack.

It is also apparent that although I have described but one embodiment of my invention, various changes and modifications can 'be made therein without departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. An immersion heating apparatus, comprising:

(a) a furnace for containing a bath of liquid metals,

(b) a tubular heat transfer member having an intermediate portion adapted for immersion in said bath and a discharge and terminating above the normal level of said bath,

(c) flame-producing means for delivering a heating flame through the intermediate portion of said heat transfer member and toward the discharge end of said heat transfer member,

(d) an insulating liner mounted Within said transfer member and adjacent the discharge end of said heat transfer member at and above the normal level of said bath, said liner having a length accommodating variations in the normal level of said bath to provide localized insulation for said tubular heat transfer member from said heating flame, and the upper end of said liner terminating short of the discharge end of said heat transfer member to form a socket for an upright exhaust stack, and

(e) a removable exhaust stack having its lower end separably seated in the socket formed by said heat transfer member and said liner.

2. The heating apparatus as defined in claim 1, wherein said exhaust stack and said insulating liner have a common inner diameter so that said exhaust stack forms a substantially smooth continuation of the inner surface of said liner in the direction of travel of the combustion products of said flame.

3. The heating apparatus as defined in claim 1, wherein said liner is formed of a ceramic material and said exhasut stack is formed of cast iron.

4. The heating apparatus as defined in claim 1, wherein said exhaust stack has a length suflicient to discharge the products of combustion of said heating flame to a position remote from the level of said bath.

5. The heating apparatus as defined in claim 1, wherein said liner is formed of a ceramic material, said exhaust stack is formed of cast iron and has a common inner diameter relative to said liner so that said stack forms a substantially smooth continuation of the inner surface of said liner and in the direction of travel of the products of combustion of said flame, and said exhaust stack has a length suflicient to deliver said products of combustion to a position remote from said bath.

6. Immersion apparatus, comprising:

(a) a furnace for containing a bath of liquid metal,

(b) a tubular heat transfer member having an inlet above the normal level of said bath and an intermediate portion downstream from said inlet and adapted for immersion in said bath,

(c) a burner assembly mounted within the inlet end of said heat transfer member with a flame producing nozzle directed toward the intermediate portion of said heat transfer member,

(d) a tubular shield supported concentrically within the inlet end of said transfer member, said tubular shield enclosing said burner assembly and having a free lower end extending below the normal level of said bath so that the portion of said heating tube at the normal level of said bath is shielded from the flame produced from said nozzle, and said tubular shield having a diameter less than the diameter of said heat transfer member, and

(e) means extending between said tubular shield and said heat transfer member above the normal level of said bath closing the upper end of said heat transfer member to form an annular dead air space between said tubular shield and said heat transfer mem her so that said dead air space locally insulates the portion of said heating tube at the normal level of said bath.

7. The heating apparatus as defined in claim 6, wherein the inner diameter of said annular air space is substantially of the outer diameter of said annular air space.

8. The heating apparatus as defined in claim 7, including said tubular heat transfer member having a discharge end downstream from said intermediate portion and supported above the normal level of said bath, an insulating liner positioned within said heat transfer member adjacent the discharge end thereof and at the normal level of said bath, said liner having a length accommodating variations in the normal level of said bath to provide localized insulation for said tubular heat transfer member from said heating flame, the upper end of said liner terminating short of the discharge end of said heat transfer member to cooperate with said heat transfer member to form a socket for a removable upright exhaust stack; and a removable exhaust stack having its lower end seated in said socket.

9. The heating apparatus as defined in claim 8, wherein said exhaust stack and said insulating liner have a common inner diameter so that said stack forms a substantially smooth continuation of the inner surface of said liner in the direction of travel of the products of combustion of said flame.

10. The heating apparatus as defined in claim 8, wherein said liner is formed of a ceramic material and said exhaust stack is formed of cast iron.

11. The heating apparatus as defined in claim 8, wherein said exhaust stack has a length sufficient to discharge the products of combustion of said heating flame to a position remote from said bath.

12. The heating apparatus as defined in claim 8, wherein said insulating liner is formed of a ceramic material,

said exhaust stack is formed of cast iron and has a com- 15 mon diameter with the inner diameter of said insulating liner so that said stack forms a substantially smooth continuation of the inner surface of said liner in the direction of travel of the products of combustion of said flame, and said exhaust stack has a length sufficient to discharge said products of combustion to an area remote from said bath.

References Cited UNITED STATES PATENTS 2,300,981 11/1942 Skolas 126-360 2,716,977 9/1955 Loyles et a1. 126360 3,078,840 2/1963 Day 126360 3,212,493 10/1965 Lacey 126-360 3,266,485 8/1966 Girton 126360 FOREIGN PATENTS 687,303 2/1953 Great Britain.

FREDERICK L. MATTESON, JR, Primary Examiner.

R. A. DUA, Assistant Examiner. 

